1. Field of the Invention
The present invention relates to an optical disc improved in data format including a user data, ID information and control information, a method of write to the optical disc and a method of read from the optical disc.
2. Description of Related Art
FIG. 1 schematically shows the data format on a conventional optical disc.
In the conventional optical disc, a user data, ID information and control information are coded as one block for error correction, and the coded data are modulated, and a sync signal added to the modulated data for write to the optical disc. Generally, the user data has been pre-coded for an error correction (EDC is added to the user data) separately from the above-mentioned error-correcting coding.
In FIG. 1, the hatched portion of the ECC structure indicates a parity, and the hatched portion of the physical structure indicates an FS (frame sync signal).
FIG. 2 shows a data format for a DVD, as an example. In this data format, one sector contains a 2-kB user data, control and ID information, and EDC. One block consists of 16 sectors, and an information word containing 16 sectors of user data, control and ID information and EDC is coded for error correction (parity is added). In the DVD, RSPC (Reed Solomon product code) is used as correcting code (in this respect, this data format for the DVD is different from that shown in FIG. 1). Assume here that the line direction is C1 and row direction is C2. C1 is RS (182, 172, 11) while C2 is RS (208, 192, 17).
The ECC block is configured as follows:
User data2048EDC4Control information6ID information6Total2064 × 16
One block of data corresponds to 16 sectors. One sector on the optical disc is composed of 26 frames each consisting of a 91-byte data. Two frames correspond to a C1 correcting code. Twenty six frames forming one sector on the optical disc correspond to thirteen C1 correcting codes, and contain 12 lines for an information word in the C2 correcting code direction and one line for the parity word.
For read from the optical disc, an FS signal is used for frame synchronization, then ID information is used for sector synchronization. Thus, data position in one block is known. So, the ID information has to be disposed in a direction of data on the optical disc. Also, it has to be disposed in the same position in each physical sector. FIG. 3 shows the ID information positioned at the bead of each physical sector, for example. On the DVD, the direction of user data is the same as on the optical disc. It should be noted that the operations such as scramble will not be described herein.
Recently, an optical disc having a lager capacity and higher transfer rate and a disc drive for such an optical disc are demanded for use to store dynamic images, etc. In particular, recordable type and rewritable disc systems have to be of a rather large capacity to assure a sufficient quality of an image since the image information cannot easily be real-time compressed at a high efficiency, which depends upon the content thereof. For such a larger capacity of the optical disc, there are available methods such as increased NA (numerical aperture) of the optical system for data write and/or read and decrease in thickness of the disc substrate to assure a sufficient skew margin, etc. However, since the increase of capacity will lead to a higher recording density of the optical disc and the decrease of the disc will cause the disc to be adversely affected by dust, it is desirable to assure the larger capacity of the optical disc by improving the capability of error correction. The optical disc should desirably be strong against a burst error among others. On the other hand, for a larger capacity of the optical disc, the coding efficiency should not be too low. For these purposes, it has been proposed to enlarge the error-correcting code, namely, increase the size of an ECC block. However, it is difficult to use the normally used PC (product code) of GF (28) in a larger ECC block than used in the DVD technology, for example, an ECC block containing more than 64 kB of user data.
An ECC block in which an LDC (long distance code; one-directional correcting code of a long distance (having many parities) is configured with a deep interleave is more suitably usable in these situations.
LDC is advantageous in that the time required for correcting operation is shorter since a single pass of correction is only required basically and write and read can be done with a high efficiency since output simultaneous with a correcting operation is enabled by disposing the direction of user data in the same direction as error-correcting code. With the user data disposed in the same direction as the error-correcting code, an error which could not be corrected can be prevented from being dispersed into a plurality of logical sectors. Because of this fact, the user code should preferably be arranged in the same direction as the error-correcting code. For use of LDC, the error-correcting code direction is set orthogonal (interleaved) to the disc direction to enhance the resistance of the optical disc against burst error. In effect, the error-correcting code should be disposed in the same direction as the user data direction but in a different direction from the disc direction.
FIG. 4 shows an example of the conventional data format to a large-capacity optical disc. In this data format, one logical sector contains a 2-kB user data, control information and EDC, and one block consists of 32 logical sectors and ID information. The block is formed from an information word consisting of the 32 logical sectors of user data (equivalent to 64 kB), control information, EDC and ID information and which is coded for error correction (parity is added). The code used is LDC.
The above can be expressed as follows:
User data2048EDC4Control information22ID information6Total2070 × 32
This content is disposed in the ECC block, and can be represented by RS (240, 208, 33)×320.
One block of data equivalent to 32 physical sectors on the optical disc. One physical sector on the optical disc consists of 10 frames each of 240-byte data.
For read from the optical disc, an FS signal is used for frame synchronization, then ID information is used for sector synchronization. Thus, data position in one block is known. So, the ID information has to be disposed in a direction of data on the optical disc. Also, it has to be disposed in the same position in each physical sector, and also in the same position in each of the physical sectors. As shown in FIG. 5, the ID information is positioned at the head of each physical sector, for example.
The user data should desirably be disposed in the same direction as on the optical disc. As seen from FIG. 4, however, the ID information interferes with this positioning so that it is difficult to dispose the logical sector in the direction of the error-correcting code. Also, a physical sector full of parity word because no ID information cannot be placed in that physical sector. Therefore, limitations have to be imposed to the data formatting so that information word and parity word can be positioned evenly in each of the physical sectors.
As mentioned above, for providing a large-capacity, high transfer-rate optical disc format and optical disc drive, it may be possible to provide the interleave length, enhance the error-correcting capability by using an error-correcting code of a large code distance (LDC) and raise the writing and reading speed by disposing error-correcting code in the same direction as user data. In this case, however, since parities in ID information and user data interference with each other, it is not easy to form such a data format.